The present invention relates to internal combustion engines and, more particularly, to a supercharged, two cycle internal combustion engine.
Heretofore various proposals have been made for increasing the thermal and mechanical efficiency of internal combustion engines. In a typical internal combustion engine, as speed increases, the amount of air/fuel mixture taken into the engine on an intake stroke or the volumetric efficiency of the engine will decrease. In normally aspirated engines, only atmospheric pressure acts to force the air/fuel mixture into the engine during the intake stroke. As engine speeds increase, the amount of air/fuel mixture entering the engine rapidly decreases. This reduction in volumetric efficiency reduces the power output and the torque output of the engine at higher engine speeds. Further, in order to insure more complete combustion of the air/fuel mixture within the combustion chamber, the ignition timing is commonly advanced. Ignition occurs prior to the power piston reaching its top dead center position. As a result, the peak pressures within the cylinder acting on the power piston during the power stroke do not occur at the optimum time for maximum torque. As the piston moves past top dead center and towards the bottom dead center position, the pressures within the cylinder fall off rapidly.
In typical two-stroke engines in which a power stroke occurs every two piston strokes or every crankshaft rotation, maximum efficiency and peak powers are not achieved due primary to incomplete exhaust of the burned air/fuel mixture. In a typical piston ported, two cycle engine, an air/fuel mixture enters the crankcase of the engine as the piston moves up to a top dead center position. As the piston moves downwardly during the power stroke, the air/fuel mixture in the crankcase is compressed and transferred through transfer passages to transfer ports. The piston clears the transfer ports and the air/fuel mixture enters the cylinder above the piston. At the same time, the piston has cleared exhaust ports to permit the burnt or spent gases to exit the engine. The incoming air/fuel mixture does not efficiently scavenge the combustion chamber or, under certain conditions, some of the incoming air/fuel mixture may exit the combustion chamber through the exhaust port prior to its being closed by the piston. This mixing of the fresh air/fuel mixture charge with the burned gases and/or the loss of the charge through the exhaust port significantly reduces the power output of the two cycle engine.
Various proposals have heretofore been made to increase the volumetric efficiency, insure more complete scavenging of the exhaust gases or to delay the achievement of peak pressures during the power stroke in order to increase the torque output of the engine. Such prior proposals have included the design of special piston configurations in order to provide staged or delayed pressure increases to compensate for the combustion chamber increase in cubic capacity during the power stroke. An example of one such piston construction may be found in U.S. Pat. No. 3,897,769, issued Aug. 5, 1975, to Jozlin, and entitled SECONDARY COMBUSTION CHAMBERS FOR INTERNAL COMBUSTION ENGINES. Another example of a modified piston construction to achieve similar results may be found in U.S. Pat. No. 2,151,218, issued Mar. 21, 1939, to Lutz, and entitled DIESEL ENGINE. These constructions, while achieving higher average or mean effective pressures, have not solved the problems related to volumetric efficiency and incomplete scavenging of the combustion chamber.
Other proposals to increase the efficiency of two cycle engines have included the use of supercharger devices. The superchargers increase the amount of air/fuel mixture which is delivered to the engine and, therefore, boost the engine power output. Superchargers have been constructed which include a compressor and a turbine linked together by a common shaft. The turbine is rotated by the exhaust gases from the engines. The compressor thereby delivers a compressed charge to the engine cylinders. The supercharger increase the charge delivered to the engine, increasing the volumetric efficiency and increases the power developed during the power stroke.
U.S. Pat. No. 2,551,478, issued May 1, 1951, to Wagers, and entitled SUPER CHARGE TWO CYCLE ENGINE WITH RETARDED FIRING discloses another type of a supercharger used with two cycles. The engine disclosed in this patent includes a main piston, a cylinder and a crankshaft arrangement and an ignition firing means which is adapted to initiate combustion after the piston has moved a considerable distance beyond top dead center. A piston/cylinder and bypass arrangement are included to force air into the main cylinder as the piston is moving beyond top dead center to compensate for compression loss due to piston movement and to supercharge the main cylinder prior to initiation of combustion. The supercharger piston is moved upwardly in a compression and transfer stroke by a cam secured to the engine crankshaft.
U.S. Pat. No. 1,751,385, issued Mar. 18, 1930, to Beaudry, and entitled INTERNAL COMBUSTION ENGINE, discloses a construction wherein a power cylinder receives a compressed air/fuel mixture from an auxiliary piston cylinder arrangement . The auxiliary piston is connected to the engine crankshaft through a connecting rod.
U.S. Pat. No. 3,675,630, issued July 11, 1972, to Stratton, and entitled ENGINE, also discloses a construction wherein a power generating cylinder receives a compressed air/fuel mixture from an auxiliary fluid compressing cylinder. The mixture or charge is ignited after the power piston in the power generating cylinder has passed and is moving away from its top dead center position. Electrically energizable solenoids are included for operating intake, exhaust and transfer valves.
British Pat. No. 815,494, published June 24, 1959, discloses a similar two cycle internal combustion engine which, however, employs the exhaust gases from the power cylinder to operate an air pump. This method of supercharging should increase engine overall efficiency since normally lost energy from the hot exhaust gases is employed as in the rotary or turbine type compressor superchargers. In one embodiment illustrated in this patent, a power piston reciprocates within a piston cylinder. The cylinder defines an intake and an exhaust port. A valve controls passage of the exhaust gases from the exhaust port to an exhaust manifold. When the valve is in a closed position, the exhaust gases act upon a piston of reduced diameter which is connected to a double acting piston of larger diameter. Valves control intake, compression and exhaust of air from the double acting piston cylinder. A smaller piston is also connected to the large piston and is received within a smaller cylinder. The smaller piston compresses air within the smaller cylinder to cushion movement of the double acting piston and also to return the double acting piston to its initial position when the exhaust valve is opened to permit exhaust gases to pass to an exhaust manifold.